She said: "I even spoke to a dentist at the practice near my work and he said it looks like a rat's tooth.

Mouth of horror: Annabel took what she thought was a piece of bone out of her mouth and washed it under a tap (Image: SWNS)

"I just don't understand how a tooth could have got in there unless there are rats running around the factory.

"I didn't see it in the food and it could've been a really bad choking hazard.

"I know things happen but I wonder how it could have got in there. It's so grim that it was in my mouth.

"I think this is the end of my lasagne days. I was probably eating ratty lasagne which is disgusting."

Ready meal :The dish Annabel was eating from Waitrose - and she says she won't buy again (Image: SWNS)

Arabella contacted Waitrose customer services, who offered an apology and said the matter is under investigation.

The upmarket store did not even offer to refund her for the £2.50 beef lasagne.

A spokesperson for Waitrose said: "We take all customer complaints seriously and are very sorry about this customer's experience.

Root of the problem: Annabel's dentist friend believes the tooth may be from a rat (Image: SWNS)

"The quality and safety of our products is our top priority and our ready meal suppliers have very strict processes to prevent materials which shouldn't be there getting into food - so we are mystified how this could have happened.

"We would like to investigate by sending the item for analysis - which we'll do as soon as we receive it."